It is known that in electrophotography and electrostatic printing, electrostatic latent images which are electrified either positively or negatively on a photoconductive layer containing a photoconductive material such as selenium, zinc oxide, cadmium, cadmium sulfide, zinc sulfide, tellurium, anthracene, carbazol compounds or polyvinyl compounds, can be converted into visible images by developing the latent images with a toner. The latent images are produced by imagewisely exposing the surface of the photoconductive layer to actinic rays. The visible images are, if necessary, transferred to a surface of a substrate, such as paper, and, then, fixed thereon by means of heat or a solvent.
The particles of the toner comprise a binder consisting of a natural or synthetic resin and a finely divided coloring agent uniformly dispersed in the binder resin. The coloring agent comprises at least one member selected from dyes and pigments.
The toner is used alone or in combination with a solid carrier comprising finely divided glass or iron particles.
When the latent positive images are electrified negatively and negatively electrified positive images are developed with toner particles electrified positively, the resultant visible images are positive. However, when the latent positive images are electrified positively and the positively electrified positive images are developed with toner particles electrified negatively, the resultant visible images are negative.
Usually, conventional dyes and pigments are capable of being electrified positively. Even if the conventional dyes and pigments are capable of being electrified negatively, the quantity of electricity on the dyes or pigments is unsatisfactory.
Also, some types of dyes and pigments are unsatisfactorily compatible with the binder resin. Therefore, when the latent images electrified positively are developed with the toner particles containing conventional dyes or pigments, the resultant visible images are not clear and, sometimes, foggy.
Also, it is known that some types of metal-containing aromatic compound are effective as a charge-controlling agent. However, conventional metal-containing charge-controlling agents are unsatisfactory as the coloring agent.
For example, U.S. Pat. No. 4,206,064 discloses a negatively electrified toner for developing electrostatic images. The toner contains a charge-controlling agent comprising at least one member selected from metal complexes of salicylic acid and metal complexes of alkyl salicylic acid. However, the above-mentioned types of metal complexes are useless as a coloring agent, and exhibit an unsatisfactory compatibility with the binder resins.